Hydrocarbon production typically requires a variety of chemical treatments. Normally injected downhole, the chemicals treat the producing formation or portions of the well. When injecting chemicals in the liquid state, the operator must compensate for dilution of the treatment chemicals by the carrier fluid. Further, certain well treatment chemicals, such as acids, require the use of additional safety procedures to protect on-site personnel and the environment.
Various chemicals and drugs are commonly encapsulated as a means for controlling the release of the encapsulated material. Current technology provides for the encapsulation of solids, gels/colloids and frozen liquids. Free flowing liquids such as water or mineral acids are not currently encapsulated in liquid form. Rather, encapsulation of free flowing liquids generally requires absorption of the liquid on a solid prior to encapsulation.
The invention disclosed herein provides a method for encapsulating free flowing fluids. In accordance with the invention, free flowing treatment chemicals are encapsulated to prevent dilution of the chemicals by the carrier fluid and to minimize safety and environmental issues. In addition, the inventive method allows placement of the well treatment chemicals at the desired downhole location without premature reaction or release of the chemicals.
The present invention is particularly useful for acid etching a fractured production zone. Following the fracturing of a production zone, well operators commonly acid etch the fracture face to enhance hydrocarbon production rates. The acid etching process involves injection of an acid downhole through the production pipe string into the fracture. Preferably, the acid penetrates the entire length of the fracture. Once in the fracture, the acid reacts with the fracture rock face creating channels in the rock face. Following the release of pressure on the fractured zone, the resulting channels provide a flow path thereby increasing the flow of hydrocarbons from the production zone to the borehole.
In accordance with the invention, the acid used in the etching process can be delivered in a safe, environmentally friendly and undiluted manner to the exact location where acid etching is desired. The invention achieves other advantages as well. For example, in prior art practices, the acid detrimentally impacts the pipe string and casing. Repeated acid treatments may require a xe2x80x9cwork overxe2x80x9d or recompletion of the well to replace those portions of the pipe string damaged by the acid. Encapsulating the acid in accordance with the invention permits injection of the acid without exposing the pipe string to the corrosive effects of the acid. Further, for example, the encapsulated acid can be delivered deeply into the fracture prior to release.
The inventive well treatment process also improves the performance and economics of other well treatment chemicals. For example, encapsulation permits the controlled release of well treatment chemicals at a desired downhole location. Therefore, where the operator previously used a large quantity of chemicals to compensate for dilution or reaction during transport, the operator may now reduce the quantity of chemicals used. Thus, as an added benefit, the operator will conserve resources, save money and reduce the risk associated with handling chemicals at the well site.
The current invention provides a method of encapsulating a liquid within a semi-permeable membrane. The method first encapsulates solid material within a semi-permeable membrane to form a capsule. The capsule is placed in a liquid capable of passing through the membrane and dissolving the solid. The solid is allowed to dissolve in said liquid. The capsule remains in the liquid for a period of time sufficient to permit concentration gradient driving forces to displace substantially all dissolved solid from within the capsule. The resulting capsule contains primarily the liquid.
The current invention also provides an alternative method for encapsulating a liquid within a semi-permeable membrane. This method encapsulates a solid within a semi-permeable membrane to form a capsule. The capsule is placed in a first liquid capable of passing through the membrane and dissolving the solid. Subsequently, the capsule containing a solution of solid and first liquid is placed in contact with a second liquid. The concentration and/or volume of the second liquid contacting the capsule, in comparison to the volume of the solution within the capsule, creates an environment in which concentration gradient driving forces will remove substantially all of the solution of first liquid and solid from the capsule. As a result, the capsule contains primarily the second liquid.
The current invention also provides a method for treating a downhole region of a well with well treatment chemicals or additives. The method encapsulates a solid within a semi-permeable membrane to form a capsule. The capsule is placed in a liquid capable of passing through the semi-permeable membrane and dissolving the solid. The solid is allowed to dissolve in said liquid. The capsule remains in the liquid for a period of time sufficient to permit concentration gradient driving forces to displace substantially all dissolved solid from within the capsule. The resulting capsule contains primarily the liquid. The liquid containing capsule is placed downhole at a preselected point. Following positioning, the encapsulated liquid is released.
Additionally, the current invention provides an alternative method for treating the downhole region of a well. This method encapsulates a solid within a semi-permeable membrane to form a capsule. The capsule is placed in a first liquid capable of passing through the membrane and dissolving the solid. Subsequently, the capsule containing a solution of solid and first liquid is placed in contact with a second liquid. The concentration and/or volume of the second liquid contacting the capsule, in comparison to the volume of the solution within the capsule, creates an environment in which concentration gradient driving forces will remove substantially all of the solution of first liquid and solid from the capsule. As a result, the capsule contains primarily the second liquid. Following placement at the desired location, the second liquid is released from the capsules.
Further, the current invention provides a method for acid etching a fracture face located in a subterranean production zone. The method provides for hydraulically fracturing a subterranean formation to produce a fractured formation having at least one fracture face. After fracturing the formation, capsules of liquid acid are injected into the fractured formation while hydraulic pressure is maintained on the formation. Typically, a carrier fluid is used to transport the capsules downhole to the fractured formation. After the capsules are deposited in the fractured formation, hydraulic pressure is released from the formation. The drop in hydraulic pressure allows the formation to close on and crush the capsules thereby releasing the liquid acid. The acid subsequently reacts with and etches the fracture face.